Application of the hottest PON in broadband optica

Application of PON in broadband optical access network

with the implementation of business transformation by fixed line operators, many operators are starting to transform the bearer to adapt to this change. After starting to transform the core, the bandwidth bottleneck of access has become increasingly prominent. Although ADSL has become the current mainstream access technology of broadband networks, it is difficult for ADSL to perform its duties if it is to provide high-definition or interactive video services. Replacing copper cable with optical fiber in the access environment can bring a series of benefits: eliminating the band of telecommunications, widening the bottleneck for polyethylene and polypropylene, which are common to consumers in life, reducing maintenance costs, making it easy to achieve business integration and provide new services, improving the reliability of information transmission and communication, facilitating system expansion, saving construction investment, and so on. It is inevitable to access broadband optical fiber, and PON technology will become the technology hotspot of broadband access in the future because of its multi service, low investment, easy maintenance and other characteristics

1. PON technology

optical fiber access can be divided into passive optical network (PON) and active optical network (AON) according to the type of relay optical devices

in optical access, if the optical wiring (ODN) is composed of passive components without any active nodes, this optical push in is PON, as shown in Figure 1. The architecture of PON is mainly to shunt the optical signal downstream of the optical fiber line terminal equipment OLT to each user terminal equipment onu/t through a passive component splitter (optical splitter). This greatly reduces the cost of network room and equipment maintenance, and saves the construction cost of a large number of optical cable resources. PON has thus become the latest popular technology of FTTH

pon technology began in the early 1980s. At present, PON products on the market are mainly divided into apon/bpon (ATM pon/broadband PON), EPON (Ethernet PON) and GPON (Gigabit PON) according to the adopted technology

2. Comparison between PON and traditional network

compared with the structure of traditional network, PON has the following advantages

(1) Po has a very decadent prospect. N does not need to install active devices between the central office and users, so it will save more initial construction costs and a lot of outdoor facility maintenance costs

(2) due to the point to multipoint access mode adopted by PON, the infrastructure cost of laying optical fibers between the central office and users is shared by users, which can improve the return on network construction investment. Compared with the method of configuring end-to-end optical fibers for each user, PON devices that provide services for the same number of customers are smaller and occupy less space in the central office

(3) PON supports both traditional services (traditional service pots, analog TV) and broadband services (IP voice transmission, IPTV, broadband, etc.)

(4) PON supports all residential users (using pots, analog TV and data services) and many commercial users (using t1/e1 and Ethernet services) to share an access (including physical layer and protocol layer), without using different access to provide services for them respectively, thus reducing the number of decentralized access

3. Several PON technologies and their comparison

apon (also known as BPON) is characterized by the ATM architecture approved by the International Telecommunication Union (ITU) in the mid-1990s. Compared with Ethernet devices, ATM switches and ATM terminal devices are quite expensive. Moreover, now Internet works in tcp/ip protocol, and user terminal devices are all IP devices. Using ATM technology, IP packets must be split and re encapsulated into ATM cells, which greatly increases the overhead of the network and wastes network resources

epon is a manufacturer driven solution based on Gigabit Ethernet passive optical network technology. The international standard ieee802.3ah was officially released in 2004

GPON is a solution designed according to the exact needs of consumers and driven by operators. Standardization is mainly driven by FSAN and ITU-T

compared with GPON technology, EPON has a lower technical threshold and the design difficulty of core chips is also low. At present, many chip manufacturers have joined the camp of EPON chip design, and the industrial chain is more mature. The meeting showed the characteristics of China's nonferrous metal materials industry and discipline

from the perspective of technical theory, GPON has more advantages than EPON. From the perspective of practicality, the comprehensive cost of GPON will be higher than that of EPON equipment due to the chip. In the next two years, with the large-scale commercial use of GPON, the cost of GPON will converge with that of EPON. However, if it is only the access of data services, EPON is enough at present

4. Application mode of g/epon

at present, the application of g/epon in China is basically in its infancy, and there are still different understandings of the application mode. In my opinion, the group mode can be divided into three types: dedicated line mode, community mode and hybrid mode

4.1 dedicated line mode

this mode is that the user network is directly connected to the ONU. Because the perfect management function of g/epon can accurately judge the obstacle points and dynamically adjust the bandwidth, users can get larger bandwidth and higher service quality assurance. At the same time, the use of passive optical devices in the intermediate link also reduces the operation and maintenance costs of operators, improves the utilization of bandwidth, and saves optical cable resources and port resources of office equipment. So far, this mode is applicable to the access of enterprise VPN groups, bars, villas and high-end residential areas

4.2 cell mode

on the premise of not changing the original optical cable network topology, this mode uses passive beam splitter to replace the original cascade connection equipment. Through the combination with Ethernet switch, DSLAM, IAD and other access equipment, it saves optical cable resources and transformation costs to the greatest extent, optimizes the network structure, solves the "bottleneck" problem of the last kilometer, and meets the user's various business access needs. This mode is applicable to the reconstruction of optical fiber cells and the comprehensive access of new cells. For rural areas with relatively scarce optical cable resources and limited user bandwidth demand, g/epon+msan mode can also be considered to save optical cable investment

4.3 mixed mode

this mode is a flexible combination of the first two modes according to the bandwidth and optical cable topology, which can effectively reduce the investment of office equipment, improve the utilization of bandwidth, and reduce the occupation of office equipment ports

in addition, the optical cable distance and access point density should also be comprehensively considered, because the transmission distance between g/epon OLT and ONU is within 20 km, and the local end equipment accounts for a large proportion of the equipment cost. Too few access points will increase the average cost of a single point, which is not as economical as bare fiber direct connection

5. Application scheme

5.1 scheme 1

a county government in Heilongjiang province needs to build an office (isolated from the Internet and dedicated to office). There are more than 20 departments in the county government courtyard, and more than 40 departments are scattered in other places. The front and back floors of the hospital are directly connected by optical fibers, and the distance between departments in the building is not more than 100 meters. Five types of cables are directly connected. Scattered departments are far away. If EPON group is adopted, the mode is as shown in Figure 2

Figure 2 EPON group

there are 9 optical fiber transfer boxes in the county. Using EPON group mode, only 10 beam splitters are used, saving more than 70 core optical fibers. The equipment investment in this way is basically the same as that of optical fiber direct connection equipment

5.2 scheme 2

a city needs urban management monitoring, and more than 300 monitoring points are required in phase I. users put forward optical fiber access requirements and adopt the optical cable direct connection scheme, as shown in Figure 3

Figure 3 urban management monitors the optical fiber direct connection group

while the EPON group is used, as shown in Figure 4

Figure 4 Comparison of the two schemes in the urban management monitoring EPON group

the EPON scheme saves a lot of metro optical cable resources, and the equipment cost is slightly higher than the direct optical connection scheme. In general, in order to save the resources of jump ring optical cable, when the optical fiber direct connection scheme is adopted, the convergence switch will be added at the OLT position, but only part of the jump ring optical cable can be saved, and the cost is basically the same as that of EPON scheme

5.3 scheme 3

an optical fiber residential community, which was originally connected to broadband users through optical fiber and LAN, now to transform the multi service bearer, it is necessary to transform the original optical cable network of the community, change the tree structure multi-level connection to the star structure, increase the bandwidth of each household and reduce the number of levels. If optical fiber +switch+iad is still used, the group mode is shown in Figure 5

Figure 5 +lan scheme of transforming optical fiber cell

and using EPON group, as shown in Figure 6

Figure 6 EPON scheme for transforming the optical fiber cell

in contrast, using the EPON group, the investment is basically the same, but there is no need to transform the optical cable in the cell. Just change the original convergence switch into a splitter, which saves the optical cable investment and reduces the number of cascading layers

6. Conclusion

with the progress of network technology, the popularization of broadband services, the introduction of triple play services, and optical fiber access are becoming more and more common. However, the unlimited expansion of pipeline and optical cable resources is impossible. The use of PON technology saves a lot of optical cable resources and effectively solves this problem. With the continuous improvement of PON technology and the continuous reduction of the cost of optical devices, the technical advantages will become more and more obvious. G/epon technology will become the main access means of FTTx services, and the application mode will be increasingly enriched in practical applications. (end)